A Survey of Nesting Colonial Waterbirds in the Hells Canyon Study Area

Von R. Pope Wildlife Technician

Technical Report Appendix E.3.2-13 January 2001 Revised July 2003 Hells Canyon Complex FERC No. 1971 Copyright © 2003 by Idaho Power Company

Idaho Power Company Nesting Colonial Waterbirds

TABLE OF CONTENTS

Table of Contents...... i

List of Tables ...... iii

List of Figures...... iii

Abstract...... 1

1. Introduction...... 2

2. Study Area ...... 3

2.1. Location ...... 3

2.2. Physiography...... 4

2.3. Land Features and Geology ...... 4

2.4. Soils...... 5

2.5. Climate...... 5

2.6. Vegetation...... 6

2.7. Land Use ...... 8

3. Plant Operations...... 8

4. Methods...... 9

4.1. Survey Design...... 9

4.1.1. Rookeries ...... 9

4.1.2. Shoreline Surveys ...... 9

4.2. Survey Methods ...... 10

4.2.1. Rookery Counts ...... 10

4.2.2. Shoreline Surveys ...... 10

4.3. Data Analysis...... 11

5. Results...... 11

Hells Canyon Complex Page i Nesting Colonial Waterbirds Idaho Power Company

6. Discussion...... 12

7. Summary and Conclusions ...... 13

8. Acknowledgments...... 14

9. Literature Cited ...... 14

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LIST OF TABLES

Table 1. Maximum number of adult colonial waterbirds observed by species and rookery, Hells Canyon Study Area, 1996–1998...... 19

Table 2. Maximum number of occupied nests by species and rookery, Hells Canyon Study Area, 1996–1998...... 19

LIST OF FIGURES

Figure 1. Areas surveyed for nesting colonial waterbirds in the Hells Canyon area, 1996–1998...... 21

Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee Dam, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border...... 23

Figure 3. Location of the Powder River rookery in the Hells Canyon Complex, 1997−1998...... 25

Figure 4. Location of the Peep Island rookery in the Hells Canyon Complex, 1996−1998...... 27

Figure 5. Number of occupied nests by species (DCCO−double-crested cormorant; GBH−great blue heron, and BCNH−black-crowned night-heron) at each rookery, Hells Canyon Complex, 1996–1998...... 29

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Page iv Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds

ABSTRACT

Surveys for nesting colonial waterbirds were conducted in the Hells Canyon Complex from 1996 through 1998. The objectives of this study were to locate existing colonies and estimate the maximum number of adults and occupied nests for each species present. Two colonial waterbird nesting colonies were located and monitored within the study area. The first, the Powder River Rookery, is located at the confluence of Eagle Creek and the Powder River with Brownlee Reservoir near Richland, Oregon. The second, Peep Island Rookery, is on an island complex in an unimpounded reach of the Snake River above Brownlee Reservoir. The Powder River Rookery was monitored from 1996 through 1998 and the Peep Island Rookery, in 1997 and 1998. Occupancy counts were conducted during the spring when adults were incubating or when juveniles were present. Three species of colonial waterbirds were documented to nest in the study area: the great blue heron (Ardea herodias), black-crowned night-heron (Nycticorax nycticorax), and double-crested cormorant (Phalocrocorax auritus). At the Powder River Rookery, only great blue herons nested. A maximum of 16 occupied great blue heron nests was documented here in 1998. All three species were observed nesting at the Peep Island Rookery. In 1998, 43 occupied double-crested cormorant nests were recorded at Peep Island, while the black-crowned night-heron and great blue heron occupied a maximum of 5 and 4 nests, respectively.

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1. INTRODUCTION

Colonial waterbirds are bird species that feed predominantly in aquatic systems and often nest close together (Speich 1986). The precarious status of colonial waterbirds indicates that most species occur in a few colonies and that available habitat is limited. Past persecution of many of these species for their feather plumes pushed many species toward extinction (Erwin et al. 1993). Surveys and censuses of colonial waterbirds are important to state and federal agencies because these species, being at the top of the food chain, are sensitive to the health of aquatic ecosystems. Therefore, numbers and reproduction of colonial nesting waterbirds can serve as indicators of the presence of artificial contaminants in the environment (Trost 1985, Speich 1986). The importance of colonial waterbirds as indicator species in Idaho justifies a census program.

The Snake River and its impoundments provide resources necessary to support a variety of nesting colonial waterbirds. In fact, from Swan Falls Dam to Farewell Bend, there are over 100 islands in the Snake River. In this section, 94 of the islands are part of the Deer Flat Wildlife Refuge. A variety of colonial waterbirds successfully nest on many of these islands. Species nesting on islands in the Snake River include the double-crested cormorant (Phalocrocorax auritus), great blue heron (Ardea herodias), black-crowned night-heron (Nycticorax nycticorax), and California gull (Larus californicus) (Trost and Gerstell 1994).

Trost and Gerstell (1994) reviewed the status of 18 colonial waterbird species in southern Idaho during 1993. Eight of the 18 species reviewed are listed as species of local or special concern. Six species are on the Blue List of the National Audubon Society (Tate 1986), including the American white pelican (Pelecanus erythrorhynchos), black tern (Chlidonias niger), double-crested cormorant, great blue heron, black-crowned night-heron, and common tern (Sterna hirundo). Birds on the Blue List are considered declining by experienced bird observers. However, the Audubon Society considers all of these species except the black tern to be of local concern. The American white pelican, great egret (Casmerodius albus), white-faced ibis (Plegadis chihi), and the black tern are considered sensitive within the states of Idaho (IDCDC 1994) and Oregon (Marshall et al. 1996). The Oregon Department of Fish and Wildlife (ODFW) also includes the Franklin’s gull (Larus pipixcan), horned grebe (Podiceps auritus), and red-necked grebe (Podiceps grisegena) as sensitive within the state of Oregon. Other colonial waterbird species that might nest in southern Idaho along the Snake River include eared grebe (Podiceps nigricollis), western grebe (Aechmophorus occidentalis), Clark’s grebe (Aechmophorus clarkii), pied-billed grebe (Podilymbus podiceps), snowy egret (Egretta thula), cattle egret (Bubulcus ibis), California gull, ring-billed gull (Larus delawarensis), Caspian tern (Sterna caspia), and Forster’s tern (Sterna forsteri) (Peterson 1977, Trost 1985, Trost and Gerstell 1994).

The study was designed to provide a general description of colonial waterbirds nesting in the Hells Canyon Complex (HCC). The objectives were to: 1) determine the location of existing colonies and 2) determine the maximum number of occupied nests per species. The Federal Energy Regulatory Commission (FERC) requires that license applicants provide descriptions of important wildlife resources occurring in project areas (FERC 1990). Colonial waterbirds are an important resource based on their ecological, recreational, sensitive, and special status qualities.

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Also, this study develops baseline data useful for any future monitoring that might be conducted by interested agencies. Reliable information describing the relative species distributions and abundances will help ensure that informed multiple-species management decisions can be made (Marcot et al. 1994).

2. STUDY AREA

2.1. Location

Hells Canyon is situated in west-central Idaho and northeastern Oregon (Figure 1). The Hells Canyon Study Area is located between the city of Weiser and the confluence of the Salmon and the Snake rivers (RM 351 to RM 188). The Snake River, a major tributary to the Columbia River, is the focal point of Hells Canyon. The river generally flows in a northerly direction and forms part of the boundary between Idaho and Oregon. The Hells Canyon Hydroelectric Complex is located on the Snake River in the southern portion of Hells Canyon and includes three reservoirs—Brownlee, Oxbow, and Hells Canyon. The reach below Hells Canyon Dam is unimpounded, although the three-dam complex controls flows.

Federal agencies, including the Bureau of Land Management (BLM) and U.S. Forest Service (USFS), are responsible for managing the majority of public land in Hells Canyon. These areas fall within the jurisdictional boundaries of the Wallowa–Whitman National Forest, Oregon; Payette National Forest, Idaho; Nez Perce National Forest, Idaho; Cascade Resource Area (RA) of the Boise District, BLM–Idaho; Cottonwood RA of the Coeur d’Alene District, BLM–Idaho; Baker RA of the Vale District, BLM–Oregon; and Northern Malheur RA of the Vale District, BLM–Oregon. Other agencies with natural resource jurisdiction in the greater project area include the USDI National Marine Fisheries Service (NMFS), USDI Bureau of Indian Affairs (BIA), USDI Fish and Wildlife Service (USFWS), and state agencies from Idaho and Oregon.

The area upstream and downstream of Hells Canyon Dam can be broadly divided into five reaches, based on distinct geomorphic features, river characteristics, and legal project boundaries:

• Upstream of Brownlee Reservoir to the Weiser Bridge (approximately 12 miles; RM 351.2 to 339.2). • Brownlee Reservoir (approximately 55 miles; RM 339.2 to 284.6). • Oxbow Reservoir (approximately 12 miles; RM 284.6 to 272.2). • Hells Canyon Reservoir Reach (approximately 25 miles; RM 272.2 to 247.0). • Downstream of Hells Canyon Dam to the confluence of the Snake and Salmon rivers (approximately 59 miles, RM 247.0 to 188.2).

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The study area below Hells Canyon Dam has limited access and very little habitat suitable for nesting colonial waterbirds. Therefore, our investigation of nesting colonial waterbirds did not include the section below Hells Canyon Dam.

In the upstream reach, the Snake River can be characterized as a low-gradient (0.2 to 0.4 m/km) river, with several island complexes. Agricultural impacts are apparent, and high amounts of irrigation returns cause higher turbidities and increased nutrient loading. Farmland and rural development on flat to gentle topography surround this reach. Brownlee Reservoir is a steep- sided reservoir with a maximum depth approaching 300 ft near the dam. Large rock outcrops occur throughout the entire length. Oxbow Reservoir is a small re-regulating reservoir surrounded by moderate to steep topography (20% to 75% slopes). Shorelines are primarily basalt outcrops and talus, except where small tributaries have created alluvial fans. Hells Canyon Reservoir is a re-regulating reservoir with maximum depths approaching 200 ft. Shorelines in the reservoir are generally very steep, and substrates are primarily composed of basalt outcrops and talus slopes. The Snake River in the downstream reach is a high-gradient river (1.8 m/km) with a wide diversity of aquatic habitat, including numerous large rapids, shallow riffles, and deep pools. Substrates are highly diverse, ranging from large basalt outcrops and boulders to cobble/sand bars. This unimpounded reach of the Hells Canyon is considered to be the deepest gorge in North America. The Hells Canyon reach is surrounded at the downstream end by nearly vertical cliff faces.

2.2. Physiography

Hells Canyon is the deepest and one of the most rugged river gorges in the continental United States. It ranges between 2000 and 3000 ft in depth from Weiser to Oxbow Dam. Below Oxbow Dam, the river enters a narrow, steep-sided chasm measuring up to 5500 ft deep. From the confluence with the Grande Ronde River, the Snake River then flows into a lava-filled basin and through a much shallower canyon to Lewiston, Idaho (USDE 1985). The elevation of the Snake River near Weiser, Idaho, is about 2090 ft msl, descending to about 910 ft msl at the confluence of the Salmon River, about 59 miles below Hells Canyon Dam.

Throughout the canyon, topography is generally steep and broken with slopes often dominated by rock outcrops and talus slopes. At the deepest points of the canyon, the walls rise almost vertically. Canyon walls are deeply dissected by numerous side canyons with tributaries to the Snake River. The Seven Devils Mountains to the east and the Wallowa Mountains to the west form the upper reaches of the canyon walls. These mountains form a series of jagged peaks reaching almost 10,000 ft, with subalpine and alpine conditions (USDA 1990) to the west.

2.3. Land Features and Geology

Hells Canyon consists of a series of folded and faulted metamorphosed sediments and volcanics overlain unconformably by nearly horizontal flows of Columbia River basalt. This basalt group covered much of eastern Washington, northern Oregon, and adjacent parts of Idaho (Bush and Seward 1992). The older rocks in the series are Permian to Jurassic in age and represent at least two episodes of island arc volcanism and adjacent marine sedimentation similar to those found

Page 4 Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds today in the Aleutian Islands west of Alaska. These rock units represent old island arc chains that were sequentially “welded” to the west coast of North America during the late Paleozoic and early to mid-Mesozoic eras by subduction of a tectonic plate beneath the North American Continental tectonic plate (Asherin and Claar 1976; USDA 1994).

In more recent geologic time, Hells Canyon was formed through erosion, by the Snake River, of the Blue Mountains in Oregon and Seven Devils Mountains in Idaho (USDE 1985). The Snake River has existed since the Pliocene and probably cut to its present level during the Pleistocene. During the Pleistocene, glacial meltwater provided abundant runoff for down- cutting, while regional uplifting created weak points in the 2000- to 3000-ft-thick basalt plateau that overlaid the Blue and Seven Devils mountains. Resulting erosion formed the currently observed drainage pattern that established the Snake River (USDE 1985). Northeast-trending, high-angle fault patterns characterize the extensive Snake River fault system running throughout the study area (Fitzgerald 1982).

Besides basalt, other rock types are also present within the study area. Extensive limestone outcrops are found in some tributary drainage areas, and local granitic outcrops also occur.

2.4. Soils

The soils throughout Hells Canyon are derived primarily from Columbia River basalt, covered in most areas with a thin mantle of residual soils from weathered native rock. Isolated areas contain deposits of windblown silt. Unconsolidated materials include ash-loess from the Mount Mazama eruption 6900 years ago, river sands and gravel deposited during the Bonneville floods 15,000 years ago, and colluvium and talus deposited more recently. The amount of soil cover declines northward through Hells Canyon. Near Hells Canyon Dam (RM 247), most rock faces are nearly vertical with little soil cover (USDA 1994).

Most soil complexes are well drained and vary from very shallow to moderately deep. Loams are the dominant textural class and vary from very stony to silty, often with a clay subsoil component (NRCS 1995).

2.5. Climate

From late fall to early spring, the climate of west-central Idaho and eastern Oregon is typically influenced by cool and moist Pacific maritime air. Periodically this westerly flow is interrupted by outbreaks of cold, dry continental air from the north, which is normally blocked by mountain ranges to the east. During the summer, a Pacific high-pressure system dominates weather patterns, resulting in minimal precipitation and more continental climatic conditions overall (Ross and Savage 1967). Hells Canyon, located in the High Desert region, is significantly influenced by the rain shadow of the Cascade Mountains to the west.

Climatological information is summarized for Weiser, Richland, Brownlee Dam, and Lewiston (Figure 2). The average annual precipitation ranges from about 380 to 500 mm (15 to 20 in), depending on elevation. It is lowest at the southern end of the study area (Weiser, 286 mm),

Hells Canyon Complex Page 5 Nesting Colonial Waterbirds Idaho Power Company increases northward (Richland, 298 mm), peaks around Brownlee Dam (445 mm), and declines toward Lewiston (326 mm). Nearly 45% of the average annual precipitation at Brownlee (445 mm [17.8 in]) falls from November through January, which strongly contrasts with the 9% average recorded for July through September. Thus, most precipitation occurs in the spring and winter (Tisdale et al. 1969, Tisdale 1986, Johnson and Simon 1987), and little or no precipitation falls during the hottest months of summer. Average annual evapotranspiration is estimated to be about 1300 mm (52 in).

Mean annual temperatures are similar among the four weather stations. Generally, the climate tends to become drier and warmer downstream of Brownlee Dam. Climatological information from Brownlee Dam (RM 284.6) is probably characteristic of the central section of the study area and discussed in more detail here. The canyon bottom area is dry with seasonal temperatures ranging from lows of about –5 ºC in January to highs of about 35 ºC in July (Figure 2). Temperatures below freezing are normally experienced from mid-November through mid-April. As a rule, winters in the canyons are mild, while summers on the canyon floor may be hot. Mean temperatures above 2000 m (6562 ft msl) elevation range from –9 ºC in January to 13 ºC in July. By contrast, mean temperatures below 1000 m (3281 feet msl) elevation range from 0 ºC in January to between 28 ºC and 33 ºC in July (Johnson and Simon 1987).

2.6. Vegetation

The types of vegetation growing along the canyon slopes of the Middle Snake River are the result of three primary ecological factors: topography, soils, and climate. Climate exerts the strongest influence on the development of plant life. The relatively mild winters below the canyon rim have allowed the development of disjunct species such as hackberry (Celtis reticulata), which is most often found in the southwestern states, though it commonly occurs in the middle and lower Snake River area (Tisdale 1979, DeBolt 1992).

Within the context of regional climate, topography is a major influence on the development and distribution of vegetation (Tisdale et al. 1969; Tisdale 1979, 1986). The topographical complexity of Hells Canyon has produced a mosaic of vegetation types (Tisdale 1979, BPA 1984, USDI 1987). Grassland, shrubland, riparian, and coniferous forest communities exist in close proximity. Interfingering of grassland and forest, for example, occurs at a number of sites throughout the canyon due to variations in aspect (Tisdale 1979).

Twenty-six cover types were identified along the Snake River in the Hells Canyon Study Area. The area that was classified covered up to approximately one mile on both sides of the Snake River or associated reservoirs. The dominant cover types were Grassland (35.5%), Shrub Savanna (21.0%), Lotic (16.1%), Shrubland (6.6%), and Cliff/Talus (5.6%). All remaining cover types covered less than 5% of the area classified.

Wetland and Riparian CommunitiesInformation is limited on wetland and riparian communities in Hells Canyon (Asherin and Claar 1976, Miller 1976, Miller and Johnson 1976, DeBolt 1992). Emergent wetland communities are composed mostly of common cattail (Typha latifolia), narrowleaf cattail (Typha angustifolia), American bulrush (Scirpus americanus), and common spikerush (Eleocharis palustris). Willows are sparsely represented, and various forbs

Page 6 Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds grow on the shoreline side of the stands (Asherin and Claar 1976). A narrow band of diverse riparian communities follows the course of the Snake River and its many tributaries. Although it is limited in geographic area, this riparian zone is vital because of the biological diversity it provides (USDI 1987). Predominant tree species in riparian areas include white alder (Alnus rhombifolia), water birch (Betula occidentalis), and black cottonwood (Populus trichocarpa). Predominant shrub species in riparian areas include syringa (Philadelphus lewisii), netleaf hackberry, chokecherry (Prunus virginiana), black hawthorn (Crataegus douglasii), and poison ivy (Toxicodendron radicans).

There is no riparian vegetation along many shoreline sections. Rather, upland vegetation on steep canyon slopes simply meets the rocky shoreline. Grassland communities are also common along the Snake River and its tributaries. Where these grassland communities occur, such as on the canyon slopes, the dominant species are bluebunch wheatgrass (Pseudoroegneria spicatum), cheatgrass (Bromus tectorum), and Idaho fescue (Festuca idahoensis) (Asherin and Claar 1976).

Herbaceous-Dominated Vegetation TypesThe dry climate and typically stony, shallow soils of the canyon have favored the development of grassland steppe communities at the lower and middle elevations (Tisdale 1979, 1986). Commonly occurring grass species in the study area include bunchgrasses such as bluebunch wheatgrass, Sandberg bluegrass (Poa secunda), and Idaho fescue (Garrison et al. 1977, BPA 1984, Tisdale 1986, Franklin and Dyrness 1988). Sand dropseed (Sporobolus cryptandrus) and red threeawn (Aristida longiseta) are also common and, at times, dominant (BPA 1984, Tisdale 1986).

Habitat types in which bluebunch wheatgrass is dominant occur throughout the study area and occupy over half of its grassland area (Tisdale 1986). Bluebunch wheatgrass flourishes on deep, loamy soils but adapts to coarser and shallower soils as well. Generally, it is associated with Idaho fescue on deeper soils and with Sandberg bluegrass on shallower soils.

Shrub-Dominated Vegetation TypesShrub species comprise a large segment of the canyon’s overall vegetation composition. Shrub-steppe vegetation types occur at mid-elevations in the Hells Canyon study area, especially in the southern region of the study area. For example, big sagebrush (Artemisia tridentata) is a dominant species in the southern sector of the study area, particularly in the area around Brownlee Reservoir (BPA 1984). Commonly occurring shrubs include big sagebrush, antelope bitterbrush (Purshia tridentata), hackberry, serviceberry (Amelanchier alnifolia), and bitter cherry (Prunus emarginata) (BPA 1984, Tisdale 1986). Other species of sagebrush are also present, including low sagebrush (Artemisia arbuscula), stiff sagebrush (Artemisia rigida), and silver sagebrush (Artemisia cana) (Tisdale and Hironaka 1981, Franklin and Dyrness 1988). For the most part, sagebrush stands are limited to the area around Brownlee Reservoir. In these stands, the herbaceous layer is dominated by Sandberg bluegrass, with a variety of forbs also occurring.

Stands of hackberry can be found throughout the study area, either on lower slopes with rocky residual/colluvial soil or on alluvial terraces with sandy soil (Tisdale 1986). In these stands, hackberry is often mixed with a number of other shrub and tree species, including antelope bitterbrush, blue elderberry (Sambucus cerulea), and ponderosa pine (BPA 1984). The herbaceous layer is most often dominated by bluebunch wheatgrass, with cheatgrass and sand

Hells Canyon Complex Page 7 Nesting Colonial Waterbirds Idaho Power Company dropseed dominant in those areas that have been heavily disturbed by the grazing and trampling of cattle.

Tree-Dominated Vegetation Types—Although coniferous forest communities are generally restricted to the higher elevations of steep canyon slopes, they do reach down to the Snake River in certain locations of the study area. The predominant forest community is a ponderosa pine (Pinus ponderosa)/bluebunch wheatgrass plant association, which extends to the river on north- facing slopes at sites along Oxbow and Hells Canyon reservoirs (Asherin and Claar 1976, Bonneville Power Administration 1984). This association typically occurs as a savanna of ponderosa pine trees distributed over a grassland steppe dominated by bluebunch wheatgrass. Shrubs are almost completely absent, except for sparsely distributed, drought-resistant species such as antelope bitterbrush and serviceberry (Garrison et al. 1977, Johnson and Simon 1987). A ponderosa pine/hackberry type may also extend down to the river in this area. Hackberry dominates the shrub layer in moderate density, and poison ivy is also abundant (Asherin and Claar 1976).

2.7. Land Use

The study area and vicinity is still dominated by the land-use patterns established at the turn of the century: irrigated and nonirrigated agriculture, livestock grazing, mining, large areas of open space, scattered rural development, and rapidly growing recreational activities. The bottomlands adjacent to the reservoirs are generally used for grazing, some farming, and recreation.

3. PLANT OPERATIONS

Hells Canyon, on the Oregon–Idaho border, is the deepest canyon in North America and home to IPC’s largest hydroelectric generating complex, the HCC. The HCC includes the Brownlee, Oxbow, and Hells Canyon dams, reservoirs, and power plants. Operations of the three projects of the complex are closely coordinated to generate electricity and to serve many other public purposes.

IPC operates the complex to comply with the FERC license, as well as to accommodate other concerns, such as recreational use, environmental conditions and voluntary arrangements. Among these arrangements are the 1980 Hells Canyon Settlement Agreement, the Fall Chinook Recovery Plan adopted in 1991, and, between 1995 and 2001, the cooperative arrangement that IPC had with federal interests in implementing portions of the Federal Columbia River Power System (FCRPS) biological opinion flow augmentation, which is intended to avoid jeopardy of the FCRPS operations below the HCC.

Brownlee Reservoir is the only one of the three HCC facilities—and IPC’s only project—with significant storage. It has 101 vertical feet of active storage capacity, which equals approximately 1 million acre-feet of water. On the other hand, Oxbow and Hells Canyon reservoirs have significantly smaller active storage capacities—approximately 0.5 and 1.0% of Brownlee Reservoir’s volume, respectively.

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Brownlee Dam’s hydraulic capacity is also the largest of the three projects. Its powerhouse capacity is approximately 35,000 cubic feet per second (cfs), while the Oxbow and Hells Canyon powerhouses have hydraulic capacities of 28,000 and 30,500 cfs, respectively.

Target elevations for Brownlee Reservoir define the flow through the HCC. However, when flows exceed powerhouse capacity for any of the projects, water is released over the spillways at those projects. When flows through the HCC are below hydraulic capacity, all three projects operate closely together to re-regulate flows through the Oxbow and Hells Canyon projects so that they remain within the 1-foot per hour ramp rate requirement (measured at Johnson Bar below Hells Canyon Dam) and meet daily peak load demands.

In addition to maintaining the ramp rate, IPC maintains minimum flow rates in the Snake River downstream of Hells Canyon Dam. These minimum flow rates are for navigation purposes and IPC’s compliance with article 43 of the existing license. Neither the Brownlee Project nor the Oxbow Project has a minimum flow requirement below its powerhouse. However, because of the Oxbow Project’s unique configuration, a flow of 100 cfs is maintained through the bypassed reach of the Snake River below the dam (a segment called the Oxbow Bypass).

4. METHODS

4.1. Survey Design

4.1.1. Rookeries

Throughout southern Idaho, the Snake River supports a number of colonial waterbird nesting sites. Literature pertaining to nesting colonial waterbirds within the study area is limited. Groves et al. (1997) and Csuti et al. (1997) illustrate the general distribution of colonial waterbirds for Idaho and Oregon respectively. However, neither publication identifies specific areas of importance. Trost and Gerstell (1994) reported the location, size, and species present for waterbird colonies throughout southern Idaho. Several colonies were located in southwestern Idaho on the Snake River. Within the study area, however, suitable habitat for colonial waterbird rookeries (that is, islands with Forested Wetlands) is limited. Well-developed riparian areas that could support colonial waterbirds colonies are limited to the Powder River pool and the unimpounded portion of the Snake River above Brownlee Reservoir. Rookeries were generally conspicuous and knowledge of their presence was determined through other wildlife surveys conducted by ground, boat, and helicopter.

4.1.2. Shoreline Surveys

In addition to monitoring colonial waterbird rookeries, we surveyed for nesting colonial waterbirds from Hells Canyon Dam to Weiser. These surveys were conducted from transects adjacent to the shoreline of Brownlee, Oxbow, and Hells Canyon reservoirs from 1996 through 1998. We divided the area into seven river/reservoir sections: 1) Upper Brownlee Reservoir

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(Farewell Bend [RM 339] to the Burnt River [RM 327]); 2) Lower Brownlee Reservoir; 3) Oxbow Reservoir; 4) Hells Canyon Reservoir; 5) Islands in the Weiser reach (RM 339 to RM 351); 6) Mainland Weiser; and 7) Powder River Pool. We excluded areas below Hells Canyon Dam because there was little suitable habitat for colonial waterbird nesting in this steep canyon. We classified river-mile segments into low, medium, and high quality habitat. High-quality habitat occurred on islands and mainland areas in the Weiser Reach and at mouths of tributaries. Medium-quality habitat was areas of shoreline with a well-developed zone of riparian vegetation. All other shoreline areas (e.g., sand, rock) were of low quality. Habitat- quality types were sampled in proportion to their availability within each section, with the goal to sample approximately 25% of the available shoreline within each river section. We randomly selected river-mile segments within each habitat-quality type. For islands, we randomly selected one side of each of the nine islands, for a total of 7.5 mi of island shoreline. The result was 55 transects covering 53.5 mi (27.8% of available shoreline): 9 islands, 5 Weiser mainland, 6 in Upper Brownlee Reservoir, 7 in the Powder River Pool, 10 in Lower Brownlee Reservoir, 7 in Oxbow Reservoir, and 11 in Hells Canyon Reservoir. Survey transects were located parallel to the shoreline, and start and end points were located in the field using topographic shoreline features.

4.2. Survey Methods

4.2.1. Rookery Counts

Rookeries were monitored each spring from 1996 through 1998. With the aid of binoculars and spotting scopes, observers recorded numbers of occupied nests, adults, and juveniles for each species present. Counts, which began on one side of the colony and progressed to the opposite side, were made from vantage points that provided clear views of the colonies (Speich 1986, Parnell et al. 1988). When possible, counts were repeated to ensure an accurate assessment of colony size. Colonial waterbird nests were considered occupied when adults were observed incubating or when juvenile birds were present. Early spring surveys coincided with incubation, when at least one adult was at the nest (Speich 1986). Although foliage made late spring surveys somewhat difficult, the presence of young in the nests confirmed nest occupancy.

4.2.2. Shoreline Surveys

Colonial waterbird surveys began in 1995 on five of the river/reservoir sections. Island and mainland transects in the Weiser Reach were added in 1996, and surveys on all seven sections were conducted in 1996 and 1997. IPC personnel conducted waterbird surveys once each year in mid June. Two observers surveyed the shoreline by traveling slowly in a boat or canoe. Observers positioned boats within 25 m of the shoreline transect and recorded nesting members of the family Podicipedidae, including the pied-billed grebe, eared grebe, western grebe, and Clark’s grebe or other colonial waterbirds that might nest in the study area. Locations of nesting colonial waterbirds were recorded by species and location. All rookeries were mapped and monitored the following spring as described above. No attempts were made to actively search for nests in the emergent vegetation and other wetland cover types lining the shore.

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4.3. Data Analysis

The number of adults and juveniles present can be difficult to determine: activity in the colony makes it challenging to obtain accurate counts. Subsequent counts may have a few more or a few less individuals than on the previous day or morning. Therefore, the maximum number of adults, juveniles, and occupied nests were reported annually for each species present at a colony.

5. RESULTS

Although several colonial waterbird nesting sites have been documented along the Snake River in southwestern Idaho, no nest sites within the study area were reported in the literature. However, two colonial waterbird nest colonies were located from transect surveys. The location of the Powder River Rookery was known before the colonial waterbird survey since it was detected during other wildlife surveys. This site is located in a grove of black cottonwoods near the confluence of the Powder River and Eagle Creek with Brownlee Reservoir at the Powder River pool west of Richland, Oregon (Figure 3). This site was observed eight times during the spring months of 1996 through 1998. The Peep Island Rookery, found in the summer of 1996, is located on a three-island complex of approximately 2.6 ha at RM 347.9 on the Snake River (Figure 4). Nesting colonial waterbirds were counted on this island complex in the spring months of 1997 and 1998. Most nesting occurred on the 0.5-ha island just west of the larger (1.6-ha) central island of the complex. A few nests are located on the small 0.5-ha island to the east. Nests in this rookery are supported by mature silver maple (Acer saccharinum), an introduced tree species common along this section of the Snake River.

The great blue heron, black-crowned night-heron, and double-crested cormorant nested in the study area (Table 1). The Peep Island Rookery was the only site where all three species nested. The double-crested cormorant was the most common colonial waterbird, with a maximum of 82 adults observed at Peep Island in 1998 and 51 in 1997. Thirteen adult black-crowned night-herons and 8 adult great blue herons were observed here in 1998. At the Powder River Rookery, the great blue heron was the only nesting colonial waterbird, with a maximum of 20 adults reported. Although a single great egret was observed at the Powder River Rookery in 1996, the species apparently did not nest there.

The number of nests occupied by great blue herons at the Powder River Rookery remained relatively stable from 1996 through 1998, ranging from a minimum of 10 in 1997 to a maximum of 16 in 1998. At the Peep Island Rookery, the number of occupied nests increased by 100% for both the double-crested cormorant and great blue heron between 1997 and 1998 (Table 2, Figure 5). In 1998, 5 black-crowned night-herons also occupied nests at the Peep Island Rookery.

With the exception of the two colonies surveyed, no other nesting colonial waterbirds were observed during shoreline transect surveys, although a number of colonial waterbirds were observed in the Hells Canyon Complex during the breeding season. The pied-billed, western, and Clark’s grebes, California and ring-billed gulls, Forster’s and Caspian tern, and American white

Hells Canyon Complex Page 11 Nesting Colonial Waterbirds Idaho Power Company pelicans have all been observed in the Hells Canyon Complex during the summer, but again, no nesting has been documented.

6. DISCUSSION

Two colonial waterbird nesting colonies were identified in this study. Both colonies were located in the upper end of the study area: one was on the Powder River arm of Brownlee Reservoir and the other in the unimpounded section of the Snake River above Brownlee Reservoir. These reaches contain the best nesting habitat for colonial waterbirds with large groves of trees and numerous island complexes.

A review of statewide distribution of breeding colonial waterbirds in Idaho (Groves et al. 1997) and Oregon, (Csuti et al. 1997) suggested only two potential nesting colonial waterbirds within the Hells Canyon Complex: the great blue heron and black-crowned night-heron. Trost and Gerstell (1994) identified several waterbird colonies on the islands contained along the Snake River in the Deer Flat Wildlife Refuge. However, no nesting colonial waterbirds were reported downstream of Weiser, Idaho, within the Hells Canyon Complex (Trost and Gerstell 1994). Further upstream, near C.J. Strike Dam on the Snake River, the same three species (great blue heron, black-crowned night-heron, and double-crested cormorant) of nesting colonial waterbirds were recorded (Pope and Holthuijzen 1997). Nesting species documented within the Deer Flat National Wildlife Refuge include the great blue heron, black-crowned night-heron, double-crested cormorant, great egret, California gull, and ring-billed gull. (Trost and Gerstell 1994).

The double-crested cormorant was the most common colonial nester in the study area. Numbers of nesting double-crested cormorants increased from 1997 to 1998. However, differences in the number of occupied nests could be attributed to the timing of the rookery counts. The 1997 count was made in early June, while the 1998 count was conducted in late April, nearly five weeks earlier in the nesting season. The early count provided a clearer view of the colony since foliage had not yet fully developed. However, the 1997 count revealed 35 double-crested cormorant nestlings that were highly visible in the nests of the rookery. Hatch and Weseloh (1999) reported that nesting numbers of double-crested cormorants have been increasing throughout much of the species range. In fact, depredation permits have been issued to control nesting double-crested cormorants in some parts of its range (Hatch and Weseloh 1999). Trost and Gerstell (1994) reported that, overall, double-crested cormorants were doing well and were probably supported by high numbers of nongame fish found in irrigation reservoirs.

Although the great blue heron is one of the most common and adaptable wading birds in North America (Butler 1992) and the most widespread members of the order Ciconiiformes in Idaho (Trost and Gerstell 1994), the species nested in relatively small numbers within the study area relative to numbers in other areas along the Snake River. At the Sand Springs Rookery on the Snake River near Hagerman, Idaho, Holthuijzen (1995) recorded as many as 172 great blue heron nests. Trost and Gerstell (1994) reported over 100 great blue heron nests on islands in the Deer Flat National Wildlife Refuge along the Snake River. These known nesting sites are located approximately 70 miles upstream from the Peep Island site. Although great blue herons have

Page 12 Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds been observed year-round throughout the study area, the amount of suitable foraging habitat probably limits the number of breeding pairs found here. Aside from the Powder River pool on Brownlee Reservoir and the upper end of Brownlee Reservoir, the study area is characterized by steep shorelines and limited shallow areas. This topography limits foraging opportunities for this species relative to areas upstream.

Nesting black-crowned night-herons in the Hells Canyon Complex were documented for the first time in 1998, when five occupied nests were counted at the Peep Island Rookery. Accurate assessment of nest occupancy is more difficult for black-crowned night-herons than for other nesting species observed because their smaller nests are often closer to the ground. Also, if surveys for other colonial nesters occur too early in the spring, black-crowned night-herons might not have established territories since they generally nest later than great blue herons after trees and shrubs have leafed out (Trost and Gerstell 1994). Inconspicuous nests and lack of census data make assessments of trend data difficult (Davis 1993). Trost (1985) expressed concern about the low numbers of black-crowned night-herons in Idaho, suggesting that numbers could be depressed due to pesticide problems. Many contaminants biomagnify, which leads to high residue levels in higher trophic-level predators, such as colonial waterbirds (Parnell et al. 1988, Davis 1993). However, numbers of nesting black-crowned night-herons have increased in portions of Idaho since 1985 (Trost and Gerstell 1994).

The Snake River and its impoundments are used for a variety of recreational activities that could impact wildlife. Parnell et al. (1988) documented disturbances of colonial nesting birds at breeding, feeding, and roosting sites. An environment free from disturbance near a rookery is critical until nestlings are able to regulate their own temperatures. Threshold distances vary, depending on type of disturbance, species, and nesting stage (Parnell et al. 1988). Recreational activities appear to be low near the two rookeries during the nesting season; in fact, no human disturbances were recorded during our surveys. Other than natural process (such as floods and wind), the only threat to these rookeries is probably limited to land development.

7. SUMMARY AND CONCLUSIONS

Two colonial waterbird colonies were identified in the study area, both located in the unimpounded reaches of the Snake River. Although a number of colonial water birds have been observed in the Hells Canyon Complex only the great blue heron, double-crested cormorant, and black-crowned night-heron were documented to nest in the study area. The three species found nesting in the HCC are nesting along the Snake River and its associated impoundments. Numbers of adults and occupied nests for each species varied considerably over the years.

The status of colonial nesting waterbirds in the Hells Canyon Complex is limited to the upper reaches where available nesting and foraging habitat are located. Because little historical information exists, data on colony locations and species can be considered baseline to be used by state and federal agencies for future surveys.

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8. ACKNOWLEDGMENTS

Natalie Sunderman Turley, Chris Murphy, Cindy McCormack, Pat Aldrich, and Rachel Woodard are acknowledged for their efforts in the field, often under adverse weather conditions. Frank Edelmann and Kelly Wilde helped collect data and improved the study design and logistics. Toni Holthuijzen reviewed the document.

9. LITERATURE CITED

Asherin, D. A., and J. J. Claar. 1976. Inventory of riparian habitats and associated wildlife along the Columbia and Snake rivers. Volume IIIA. College of Forestry, Wildlife and Range Sciences, University of Idaho, Moscow, ID. 556pp.

Bonneville Power Administration (BPA). 1984. Hells Canyon environmental investigation. Prepared by CH2M-Hill, Boise, ID. 300pp.

Bush, J. H., and W. P. Seward. 1992. Geologic field guide to the Columbia River Basalt, northern Idaho and southeastern Washington. Information Circular 49. Idaho Geographical Survey, University of Idaho, Moscow, ID. 35pp.

Butler, R. W. 1992. Great blue heron (Ardea herodias). In A. Poole and F. Gill, eds. The birds of North America. No. 25. The Acad. Nat. Sci., Philadelphia and the American Ornithologist’s Union. Washington, D.C. 20pp.

Csuti, B., A. J. Kimerling, T. A. O’Neil, M. M. Shaughnessy, E. P. Gaines, and M. M. P. Huso. 1997. Atlas of Oregon wildlife. Oregon State University Press, Corvallis, OR. 492pp.

Davis, W. E. 1993. Black-crowned night-heron (Nycticorax nycticorax). In A. Poole and F. Gill, eds. The birds of North America. No. 74. The Acad. Nat. Sci., Philadelphia and the American Ornithologist’s Union. Washington, D.C. 20pp.

DeBolt, A. 1992. The ecology of Celtis reticulata Torr. (Netleaf hackberry) in Idaho. M. Sc. Thesis. Oregon State University, Corvallis, OR.

Erwin, R. M., P. C. Frederick, and J. L. Trapp. 1993. Monitoring of colonial waterbirds in the United States: needs and priorities. Pages 18−22 in M. Moser, R. C. Prentice, and J. van Vessem, eds. Waterfowl and wetland conservation in the 1990’s—a global perspective. Proceedings of the International Waterfowl and Wetlands Research Bureau Symposium, St. Petersburg Beach, FL. International Wetlands Research Bureau Special Publ. 26, Slimbridge, U.K.

Federal Energy Regulatory Commission (FERC). 1990. Final environmental impact statement for Milner (FERC No. 2899), Twin Falls (FERC No. 18), Auger Falls (FERC No. 4797), and Star Falls (FERC No. 5797) Hydroelectric Projects, Idaho. Washington, D.C.

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Fitzgerald, J. F. 1982. Geology and basalt stratigraphy of the Weiser Embayment, west-central Idaho. Pages 137-141 in Cenozoic geology of Idaho, B. Bonnichsen and R. M. Brechenwage, eds. Idaho Bureau of Mines and Geology, University of Idaho, Moscow, ID.

Franklin, J. F., and C. T. Dyrness. 1988. Natural vegetation of Oregon and Washington. Oregon State University Press. 452pp.

Garrison, G. A., A. J. Bjugstad, D. A. Duncan, M. E. Lewis, and D. R. Smith. 1977. Vegetation and environmental features of forest and range ecosystems. U.S. Dep. Agric., For. Serv., Agric. Handb. No. 475. 68pp.

Groves, C. R., B. Butterfield, A. Lippincott, B. Csuti, and J. M. Scott. 1997. Atlas of Idaho’s Wildlife. Idaho Dep. Fish and Game, Nongame and Endangered Wildlife Program, Boise, ID. 372pp.

Hatch, J. J., and D. V. Weseloh. 1999. Double-crested cormorant (Phalocrocorax auritus). In A. Poole and F. Gill, eds. The birds of North America. No. 441. The Birds of North America Inc., Philadelphia, PA. 36pp.

Holthuijzen, A. M. A. 1995. An investigation of colonial waterbirds in the Hagerman study area. New License Application: Upper Salmon Falls, Lower Salmon Falls, and Bliss hydroelectric projects. Technical Report E.3.2-G. Idaho Power Company, Boise, ID. 20pp.

Idaho Conservation Data Center (IDCDC). 1994. Rare, threatened and endangered plants and animals of Idaho. 3rd ed. Idaho Dep. Fish and Game, Boise, ID. 39pp.

Johnson, C. G. Jr., and S. A. Simon. 1987. Plant associations of the Wallowa–Snake province, Wallowa–Whitman National Forest. U.S. Dep. Agric. U.S. For. Serv. PNR. R-6 ECOL-TP-225A-86. 272pp.

Marshall, D. B. , M. W. Chilcote, and H. Weeks. 1996. Species at risk: sensitive, threatened, and endangered vertebrates of Oregon. 2nd ed. Oregon Department of Fish and Wildlife, Portland, OR.

Marcot, B. G., M. J. Wisdom, H. W. Li, and G. C. Castillo. 1994. Managing for featured threatened, endangered, and sensitive species and unique habitats for ecosystem sustainability. U.S. Dep. Agric, U.S. For. Serv., Pacific Northw. Res. Sta., Portland, OR. PNW-GTR-329. 39pp.

Miller, T. B. 1976. Ecology of riparian communities dominated by white alder in western Idaho. University of Idaho, Moscow, ID. 154pp.

Miller, T. B., and F. D. Johnson. 1976. Ecology of riparian communities dominated by white alder in western Idaho. Pages 11−123 in Proc. terrestrial and aquatic vegetation. E. Wash. State Coll., Cheney, WA.

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Natural Resources Conservation Service (NRCS). 1995. Soil survey for Adams and Washington counties, Idaho. Weiser, ID.

Parnell, J. F., D. G. Ainley, H. Blokpoel, B. Cain, T. W. Custer, J. Dusi, S. Kress, J. A. Kushlan, W. E. Southern, L. E. Stenzel, and B. C. Thompson. 1988. Colonial waterbird management in North America. Col. Waterbirds 11:129−169.

Peterson, L. A. 1977. Colonial waterbirds in Idaho. Special Report to Idaho Dep. Fish and Game. Idaho Dep. Fish and Game, Boise, ID. 38pp.

Pope, V. R. and A. M. A. Holthuijzen. 1997. Determination of the existence of colonial waterbird colonies and numbers of nesting pairs in the C.J. Strike Study Area. New License Application: C.J. Strike hydroelectric project. Technical Report E.3.2-E. Idaho Power Company, Boise, ID. 20pp.

Ross, S. H., and C. N. Savage. 1967. Idaho earth science: Geology, fossils, climate, water, and soils. Idaho Bureau of Mines and Geology, University of Idaho, Moscow, ID. Earth Science Series No. 1. 271pp.

Speich, S. M. 1986. Colonial waterbirds. Pages 387−405 in A. Y. Cooperrider, R. J. Boyd, and H. R. Stuart, eds. Inventory and monitoring of wildlife habitat. U.S. Dept. Inter., Bur. Land Manage., Serv. Cen., Denver, CO.

Tate, J. 1986. The blue list for 1986. Am. Birds 40:202−207.

Tisdale, E. W. 1979. A preliminary classification of Snake River canyon grasslands in Idaho. For., Wildl. and Range Exp. Sta., University of Idaho, Moscow, ID. 8pp.

Tisdale, E. W. 1986. Canyon grasslands and associated shrublands of west-central Idaho and adjacent areas. For., Wildl and Range Exp. Sta., University of Idaho, Moscow, ID. Bull. No. 40. 42pp.

Tisdale, E. W., and M. Hironaka. 1981. The sagebrush-grass region: a review of the ecological literature. For., Wildl. and Range Exp. Sta., University of Idaho, Moscow, ID. 31pp.

Tisdale, E. W., M. Hironaka, and M. A. Fosberg. 1969. The sagebrush region in Idaho: a problem in range resource management. Ag. Exp. Sta., University of Idaho, Moscow, ID. Bull. No. 512. 12pp.

Trost, C. H. 1985. Status and distribution of colonial nesting waterbirds in Idaho. Special Report to Idaho Dep. Fish and Game. Idaho Dept. Fish and Game, Boise, ID. 74pp.

Trost, C. H., and A. Gerstell. 1994. Status and distribution of nesting waterbirds in southern Idaho, 1993. Special Report to the Nongame and Endangered Wildlife Program. Idaho Dept. Fish and Game. Boise, ID. 106pp.

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U.S. Department of Agriculture (USDA). 1990. Final environmental impact statement, land and resource management plan. U.S. Dep. Agric., For. Serv., Pacific Northwest Region, Wallowa-Whitman National Forest, Baker, OR. 562pp.

U.S. Department of Agriculture (USDA). 1994. Final environmental impact statement: Wild and Scenic Snake River recreation management plan. U.S. Dept. Agric., For. Serv., Hells Canyon Nat. Rec. Area, Pacific Northwest Region, Wallowa–Whitman National Forest, Baker, OR.

U.S. Department of Energy (USDE). 1985. Final report: Hells Canyon environmental investigation. US Dep. Energy, Bonneville Power Admin., Office Power and Resour. Manage. DOOE/BP-11548-1.

U.S. Department of the Interior (USDI). 1987. Proposed resource management plan and final environmental impact statement: Cascade Resource Area. U.S. Dep. Inter., Bur. Land Manage., Boise Distr., Boise, ID.

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Table 1. Maximum number of adult colonial waterbirds observed by species and rookery, Hells Canyon Study Area, 1996–1998.

Powder River Peep Island Year Year Species 1996 1997 1998 1996 1997 1998 Double-crested Cormorant 0 0 0 N/S 51 82 Great Blue Heron 20 13 17 N/S 3 8 Black-crowned Night-heron 0 0 0 N/S 2 13 Great Egret 1 0 0 N/S 0 0

N/S—Not Surveyed

Table 2. Maximum number of occupied nests by species and rookery, Hells Canyon Study Area, 1996–1998.

Powder River Peep Island Year Year Species 1996 1997 1998 1996 1997 1998 Double-crested Cormorant 0 0 0 N/S 19 43 Great Blue Heron 15 10 16 N/S 2 4 Black-crowned Night-heron 0 0 0 N/S 0 5

N/S-Not Surveyed

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Weiser 2 SEa (641m)b 10.1d 286mme Richlanda (675m)b 10.6d 298mme 60 60 60 60 55 55 55 55 50 47, 47c 50 50 49, 49c 50 45 45 45 45 42.8i 42.8i 40 40 40 l 40 35 35 35 35 33.4h 33.8h 30 n l 30 30 n 30 25 25 25 25 20 20 20 20 15.7j 17.3j 15 15 15 15 10 10 10 m 10 5 5 5 k 5 k m (mm) PRECIPITATION (mm) PRECIPITATION 0 0

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Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee Dam, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border.

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W McRea e s Weise t Island la k e Is la n d Peep Island Rookery

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18 16 14 12 10 8 6 4 # Occupied Nests 2 0 1996 1997 1998 YEAR

Powder River Rookery

60 DCCO 50 GBHE 40 BCNH 30 20 10 # Occupied Nests 0 1996 1997 1998 YEAR

Peep Island Rookery

Figure 5. Number of occupied nests by species (DCCO−double-crested cormorant; GBH−great blue heron, and BCNH−black-crowned night-heron) at each rookery, Hells Canyon Complex, 1996–1998.

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